Tomato SlAN11 regulates flavonoid biosynthesis and seed dormancy by interaction with bHLH proteins but not with MYB proteins

Abstract

The flavonoid compounds are important secondary metabolites with versatile human nutritive benefits and fulfill a multitude of functions during plant growth and development. The abundance of different flavonoid compounds are finely tuned with species-specific pattern by a ternary MBW complex, which consists of a MYB, a bHLH, and a WD40 protein, but the essential role of SlAN11, which is a WD40 protein, is not fully understood in tomato until now. In this study, a tomato WD40 protein named as SlAN11 was characterized as an effective transcription regulator to promote plant anthocyanin and seed proanthocyanidin (PA) contents, with late flavonoid biosynthetic genes activated in 35S::SlAN11 transgenic lines, while the dihydroflavonol flow to the accumulation of flavonols or their glycosylated derivatives was reduced by repressing the expression of SlFLS in this SlAN11-overexpressed lines. The above changes were reversed in 35S::SlAN11-RNAi transgenic lines except remained levels of flavonol compounds and SlFLS expression. Interestingly, our data revealed that SlAN11 gene could affect seed dormancy by regulating the expressions of abscisic acid (ABA) signaling-related genes SlABI3 and SlABI5, and the sensitivity to ABA treatment in seed germination is conversely changed by SlAN11-overexpressed or -downregulated lines. Yeast two-hybrid assays demonstrated that SlAN11 interacted with bHLH but not with MYB proteins in the ternary MBW complex, whereas bHLH interacted with MYB in tomato. Our results indicated that low level of anthocyanins in tomato fruits, with low expression of bHLH (SlTT8) and MYB (SlANT1 and SlAN2) genes, remain unchanged upon modification of SlAN11 gene alone in the transgenic lines. These results suggest that the tomato WD40 protein SlAN11, coordinating with bHLH and MYB proteins, plays a crucial role in the fine adjustment of the flavonoid biosynthesis and seed dormancy in tomato.

REVERSAL OF RDO5 1, a Homolog of Rice Seed Dormancy4, Interacts with bHLH57 and Controls ABA Biosynthesis and Seed Dormancy in Arabidopsis

“…It was previously reported that two bHLH TFs, SPATULA (SPT) and PHYTOCHROME INTERACTING FACTOR1 (PIF1), control seed germination and GA3OX expression in response to light and temperature signaling in Arabidopsis (Penfield et al, 2005;Oh et al, 2006). bHLH TFs also function in seed dormancy in other plant species (Gao et al, 2018;Zhao et al, 2019). These findings collectively demonstrate the conservation and diversity of the bHLH gene family in the control of dormancy.…”

Genome-Wide Analysis of Basic Helix-Loop-Helix (bHLH) TFs in Sea Buckthorn (Hippophae rhamnoides)

“…Based on the highly conserved domains and their evolutionary relationships, this superfamily is mainly divided into 20-25 subfamilies in agronomically important plants. A wide range of extensive studies have been reported on the bHLH superfamily-related genes in plant species after genome sequences have been produced, including cucumber [5], Arabidopsis [7], apple [10], tomato [24] and Carthamus tinctorius [32]. Additionally, functional and structural characterizations of most plant bHLH proteins have been described in detail.…”

“…The bHLH genes also regulate plant response to various abiotic stresses, such as drought [12][13][14], salinity [15][16][17], cold [18][19][20], aluminum and iron de ciency [21][22][23]. In addition, the bHLH genes play an important role in regulating multiple signal transduction pathways and impacting biosynthesis [24,25].…”

Optimizing shelf life conditions for anthocyanin-rich tomatoes

“…Among the regulatory genes, a primary role is carried out by those encoding the R2R3 MYB, the bHLH and the WD40 proteins participating in the MBW complex [ 25 , 56 ]. Most of the genes already known to be involved in the anthocyanin synthesis in tomato [ 1 , 26 , 27 ] appeared to be expressed in Aft/Aft atv/atv fruits at the time of collection and also during storage ( Fig 5 ). Only after three weeks of storage in the dark, we measured a general reduction of the mRNA level in tomato peel, attested by the low level of expression of many genes analyzed ( Fig 5 ).…”

“…SlAN1 and SlJAF13) and WD40 proteins (e.g. SlAN11) have been identified as possible candidates for the MBW complex regulating anthocyanin synthesis in tomato [ 1 , 26 , 27 ].…”